1. Field of the Invention
This application relates to a novel detector for sensing the presence of a fluid, especially a liquid, in a tube or similar restricted vessel which has a wall that will transmit light. More particularly, it relates to such a detector which employs an improved package for a light source and detector and simplified sensing electronics.
2. Description of the Prior Art
A variety of optical sensors for liquids are known in the art. For example, such optical sensors are shown in the following issued U.S. Pat. Nos. 3,209,596, issued Oct. 5, 1965 to Kelly; 3,459,303, issued Aug. 5, 1969 to Brenchley; 3,516,284, issued June 23, 1970 to Lockard; 3,697,185, issued Oct. 10, 1972 to Kassel et al.; 3,787,703, issued Jan. 22, 1974 to Topol; 3,908,129, issued Sept. 23, 1975 to Akers; 4,150,299, issued Apr. 17, 1979 to Kasiewicz et al.; 4,227,814, issued Oct. 14, 1980 to Soodak et al.; 4,244,364, issued Jan. 13, 1981 to Grushkin; 4,303,336, issued Dec. 1, 1981 to Cullis; 4,418,576, issued Dec. 6, 1983 to White; 4,576,477, issued Mar. 18, 1986 to Corbet et al. The state of the art of such optical sensors is further shown by West German Patent No. 3,034,874, issued Mar. 10, 1985 to Eckli and in Byte Magazine, January 1986, page 276.
A problem with respect to the sensor in the Byte article in particular is that discrete resistors in the detector circuit must have their value selected for each LED light source and phototransistor pair used in such a sensor. As a result, the detector there is not amenable to mass production. The Byte article further does not discuss orienting the light source and photodetector in the light path. The lack of detail in this respect provides insufficient information for building the device mentioned there. These prior art sensors typically require custom fabrication of at least one precision component in their optical paths. A further problem with the above prior art sensors in general is that the complexity of their detector circuits does not allow them to be made as small as would be desirable for many applications.